Search

We present a statistical model for the radio range between robots in a Mobile Ad hoc NETwork (MANET) deployed in an underground mine. Such unmanned mobile robotic networks could potentially be used in hazard mitigation and search and rescue in tunnel environments such as mines and subways, as well as in building environments. In addition to fading characteristics, our model is able to represent the variable nature of the propagation path-Loss exponent. To support our model, we present path-loss measurements made in a real mine. The usefulness of our model lies in the fact that it represents an overall propagation model for a mine and therefore can be used to calculate the wireless connectivity probability of an arbitrary node in the network without requiring a detailed physical representation of the MANET within the mine. Index Terms--Mine tunnels, path-loss exponent, path-loss model, radio propagation, wireless connectivity.

In this paper, a single-phase high-frequency AC (HFAC) microgrid is shown as a novel solution towards integrating renewable energy sources in a distributed generation system. Better utilization of the Microgrid is achieved by solving power flow and power quality issues using p-q theory-based active filtering called universal active power line conditioner and unified power quality conditioner, respectively. A distributed intelligent energy management system (DIEMS) is implemented to optimize operating costs. As the optimization greatly depends on the power generation and the power output from renewable sources strongly depends on the weather, the forecast of power generation is required for DIEMS. A Fuzzy ARTMAP neural network is used to predict hourly day-type outputs based on which generation can be forecasted. Depending on the forecast, an optimization scheme is developed utilizing linear programming along with heuristics. The results obtained show the successful implementation of HFAC Microgrid with adequate power flow and power quality control, as well as the optimization of operation cost by the DIEMS with Fuzzy ARTMAP-based day-type forecasting. The improvement in the battery life is also achieved due to optimization of storage charge states using the proposed DIEMS. Index Terms--Active filters, distributed intelligent energy management system (DIEMS), fuzzy ARTMAP, high-frequency AC (HFAC), linear programming, microgrid, unified power quality conditioner (UPQC), universal active power line conditioner (UPLC).

In this paper, we compare two X-band high-efficiency switched-mode amplifiers designed around two commercially available packaged MESFET's, one having a four times larger gate periphery than the other. The amplifiers using the larger and smaller devices are designed to operate in classes E and F, respectively. The smaller device gives 685-mW output power with 7.4-dB gain and 64% overall efficiency. The larger device gives 1.70-W output power with 5.3-dB gain and 57% overall efficiency. This gives an internal (or chip-level) power-combining efficiency for the larger device of 89% in terms of overall efficiency. This is compared to the combining efficiency of circuit and spatial power combining using high-efficiency amplifiers, with the goal of assessing which architecture is the most efficient in terms of total dissipated power (dc and RF). Index Terms - Power amplifiers, power combining, high efficiency.

We demonstrate 260 GHz (λ=1.15 mm) near field imaging using a conical Teflon probe whose tip protrudes through an aperture in a tapered aluminum holder. The imaging system is based on a quasioptical millimeter wave vector network analyzer. We present a variety of different imaging examples of dielectrics and metals, in both reflection and transmission modes, as well as an analysis of interesting diffraction and scattering effects observed in some of the images. The probe has an approximate tip diameter of 0.17 mm and an aperture size of about 1 mm. We observe horizontal resolution ranging from 0.2–0.5 mm depending on the sample being imaged. [ABSTRACT FROM AUTHOR]

Modern communication signals have time-varying envelopes with significant peak-to-average ratios, resulting in low average efficiency when amplified by commonly used linear power amplifiers (PAs). For linear amplification with increased average efficiency, the Kahn envelope-elimination-and-restoration method uses a highly efficient saturated PA. In this paper, an 8.4-GHz class-F PA with 55% maximum instantaneous efficiency at 610-mW output power, is experimentally characterized in several different biasing modes. Operated in linear mode with constant drain bias, this PA has 10% average efficiency. The suppression of two-tone intermodulation products is 27 dBc when operated at about 0.7 times the peak output power. For the same PA operated in a modified Kahn mode with drive and bias control, a comparable linearity (27.7 dBc) can be obtained at peak output power. Furthermore, the average efficiency increased to 44%, a factor of 4.4 over the linear fixed bias mode.

Time-domain measurements of the output waveforms of two 8-GHz high-efficiency power amplifiers, a 1-GHz frequency doubler, and a 5-GHz frequency doubler are presented in this paper. A new photoconductive probe has enabled nonintrusive time-domain voltage measurements, which confirm switched-mode class-E and class-F amplifier operation. In order to analyze nonlinear amplifiers designed to deliver a sinusoidal wave to the load, voltages at characteristic points inside the circuit need to be known. In multipliers, waveform measurements track harmonic leakage, expediting the design cycle. The high-impedance probe used here is an optoelectronic sampler, which can sense the charge on an exposed interconnect or the field associated with a buried interconnect. These electric-field data are then converted into voltage. Index Terms--High efficiency, power amplifiers, optical sampling, transistor multipliers.

Tunnels are a challenging environment for radio communications. In this paper we consider the use of autonomous mobile radio nodes (AMRs) to provide wireless tethering between a base station and a leader in a tunnel exploration scenario. We propose a tethering algorithm for AMR motion control based on a consensus variable protocol. Using radio signal strength measurements, the AMRs autonomously space themselves so as to achieve equal radio distance between each entity in the chain from the base station to the leader. Experimental results show the feasibility of our ideas. [ABSTRACT FROM PUBLISHER]